Annealing



Patented Dec. 9, 1930 UNITED STATES PATENT OFFICE JOHN R. CAIN, OFWASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO THE RICHARD SON COMPANY,OF LOCKLAND, OHIO, A CORPORATION OF OHIO ANNEALING Application filedAugust 2, 1927. Serial No. 210,131.

My invention relates to that type of annealing which utilizes a hot bathof liquid into which the metal to be heat-treated is immersed, and ithas particular reference to the use of substances which protect themetal from oxidation or scale during the annealing operation, and to theprovision of a temperature gradient in the annealing bath, as will bedescribed.

As set forth in my application for patent on Process of heat treatingcopper and its com mercial allo s, Serial No. 116,723, filed June 17,1926, I ave discovered that for the annealing of certain metals whichundergo a change in crystalline structure at comparatively lowtemperatures, a'bath of hydrocarbon oil heated to the requiredtemperature is particularly advantageous in that, to economy and ease inhandling, there is added absolute protection from oxidation and scaleand an action which I believe to be of a reducing character, in that coper oxide coatings are apparently freed 0 their oxygen content.

The provision of heat in my oil annealing processes may be appliedeither to theoil containing vessel or to the metal being treated whereit is paramagnetic, by the use of an electrical induction heater.

1 have found that hydrocarbon oil is not readily heated by convection(internal heat transfer) currents, and this property makes such oil ofparticular value in my present process.

It is the object of my process to be described herein to permit theannealing of metal objects in baths of molten metal at temperatureshigher than are possible with hydrocarbon oil or other fluid, while atthe same time securing for my metal objects the protection fromoxidation and scale and the advantages of the reducing atmosphere whichI have found that hydrocarbon oil gives.

It is a further object of my invention to provide in an annealingapparatus a temperature gradient such that, starting with cold metalobjects, I can gradually heat them up to the proper temperature forintroduction into tie ot zone of my annealing apparatus while at thesame time protecting them effectively, then anneal them at the propertemperature for the proper length of time, and finally withdraw and coolthem gradually under conditions of equal protection.

It is a further object of my invention to provide in an annealingapparatus zones of varying but comparatively constant temperatures sothat the same apparatus will serVe for annealing operations carried onat different temperatures and will be adapted to a wide range ofarticles and materials.

I accomplishmy objects by that certain construction and arrangement ofparts to be hereinafter more specifically pointed out and claimed.

In the drawings Figure 1 illustrates diagrammatically an annealingapparatus for the handling of. small articles, while Figure 2illustrates, also diagrammatically, an apparatus suitable for thesemi-continuous annealing of metal sheets such as sheets of brass oriron.

Referring to Figure 1, I have shown a vessel 1 for holding the liquidmedia in which I propose to do my annealing The lower part of thisvessel is placed within a furnace or other source of heat, preferably aresistance electric furnace. which I have illustrated diagrammaticallyas consisting of a base 2 and refractory core 3, wound with nichromewire 4. It will be understood that the furnace will be suitably housedand insulated after the best practices in that art. I may, if desired,support my vessel upon a block of refractory material 5, so that thelowermost part of my vessel is located in the hottest part of thefurnace.

I place within the vessel 1 a mass of lead which will be melted by theheat and will form a body of liquid 6, extending both within and withoutthe heating region of the furnace. Above this I place a body ofhydrocarbon oil 7. This apparatus is suitable for the annealing of brassor alloy objects or of thin sheets of iron or steel. The lead ismaintained in its lowermost position at a temperature sufficient toaccomplish the heat-treating efiects desired upon the particular metal.There will be some tendency for the temperature of the molten lead bathto be evened by convection currents as well as conduction, but I findthat convection currents in baths of molten lead do not operate withsufficient rapidity to bring about any very marked equalization of termerature.

Furt ermore, the upper end of that portion of the vessel 1, whichcontains the molten lead, is situated outside of the. furnace and theloss of heat due to radiation is quite sufficient to offset thetemperature-equalizing effects of conduction and convection. Thus therewill be a considerable even temperature gradient from the bottom of thevessel to the top of the column of molten lead so that above this columnof molten lead I may maintain a column of hydrocarbon oil 7 in such away that a temperature gradient exists throughout it also.

I may vary the-length of my vessel 1, and consequently the lengths ofthe columns of lead and oil, in any manner desired to secure thenecessary temperature gradient. The lengths of with the size of thevessel 1, thickness and thermo-conductivity of its walls, andatmospheric or other conditions surrounding the upper part of thevessel, as well as with the degree ofheat desired in the lower part ofthe lead column. It will be obvious, however, that the other factorsremaining constant, the heat of the furnace may be so regulated as togive not only a proper annealing temperature in the anneahng zone, but acorrect and gradual temperature gradient throughout the entire annealingapparatus.

For example, with certain brasses or alloys I may prefer to start withan initlal temperature in the upper limit of the hydrocarbon oil columnof, say 200 to 250 degrees centigrade. The temperature progressivelyincreases downward until in the lower portion of the lead bath atemperature of 800 to 850 degrees centigrade is reached. In annealingcopper, brass, bronze or other alloy articles, it will be obvious thatwhenthese are immersed in the oil and lowered to the bottom of thevessel, the temperature thereof will gradually be raised from 250 to 800degrees centigrade.

The heat treatment at this point maybe continued for as long as desired,after which the articles are withdrawn slowly and are cooled downthrough the column of liquids until where they emerge from the surfaceof the hydrocarbon oil they have fallen to 250 degrees centigrade orless, so that no scaling or oxidation need be feared.

Those familiar with the art of annealing will recognize that thisapparatus is capable not only of providing sufficient degreeof thesecolumns will naturally vary heat for hcat-treating operations, but ofproviding means whereby this heat may be gradually applied and'graduallywithdrawn to secure the desired changes in the crystalline structure ofmetals or alloys.

It will be apparent also that during the heating operation my metalobjects are protected from oxidation and scaling and are surrounded bywhat amounts to a reducing atmosphere in the h drocarbon oil. From this,they pass to the ead bath and are given the required heat treatment andare subsequently cooled under conditions of equal protection byre-passage through the hydrocarbon oil.

As pointed out above, the hydrocarbon oil acts in part as a heatinsulator, so that it is even less affected by convection currents orconduction of heat than is the lead.

I prefer to employ hydrocarbon oil which can stand degrees of heat upto400 degrees centigrade; but it is possible for the lead at thejuncture of the two liquid columns to be at a" temperature somewhathigher than this, for, unless the heat is excessive, there will simplyoccur some ebullition at the surface e lead tending to restore theevenness of of t the temperature gradient and tending to protect thebody of the hydrocarbon from further ebullition or decomposition. Unlessthe heat of the lead bath is excessive, therefore, or the column ofhydrocarbon oil 7 very short, such ebullition as results involatilization of the hydrocarbon oil will simply re-' sult in theproduction of bubbles which will be condensed before they reach thesurface of the oil so that actual losses of material are unimportant. Itwill be further obvious that the body of hydrocarbon oil protects thesurface of the column of lead from oxidation.

In Figure 2 I- have illustrated dia rammatically an apparatus comprisinga ifierent form of vessel 1a, supported upon a base 2a, above a furnace311, which may be fired by coal, fuel oil, etc. The vessel 1a is ofgenerally rectangular shape but has a cylindrical bottom such as willfacilitate the passage of sheets introduced into the vessel at one sidebeneath a baflle 8, dipping down into the liquids contained in vessel 1and up again on the other side of saidbafile. The vessel will containa-body of liquid lead 6 and a body of hydrocarbon oil 7 superposedthereon. To secure the necessary temperature gradient, the columns ofmetal and oil may be varied at will, by changing the depth of the vessel1.

The function of the baflle is to provide a means for the positivesubmergence of metal articles to the hot zone of the annealingapparatus. It further tends to divide the annealing chamber and, to' adegree, prevent convection and conduction of heat.

It will be obvious that m invention is not limited to a combination 0lead and hydrocarbon oil, but may be employed in many ways with manysubstances.

In achieving a proper temperature gradient I may find it advisable toemploy more than two liquids, all or none of which may be of a metalliccharacter; or in addition to hydrocarbon and metal, I may prefer to usealso a colunm of liquid formed by the fusion of a metallic salt or otherchemical compound.

n will be obvious to those skilled in the art that in employing moltenmetals for annealing purposes the metals should be of such characterwith reference to the metal articles to be annealed as will have notendency at the temperatures used to form an alloy therewith.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is

taining a temperature gradient in a liquid annealing medium ranging froma temperature at least as high as that necessary to effect the desiredheat treatmentto a temperature at least as low as will permit withdrawalof a heat treated article to the air without danger of the formationofscale or oxide thereon, advancing an article from a cooler portion ofsaid liquid medium to a heat treating zone therein, holding said articlein said zone for a length of time necessary to efi'ect a desired heat.treatment, then withdrawing said article from said zone throu h a coolerportion of said liquid, said liquid medium comprising a plurality ofimmiscible heat resistant. liquids.

JOHN R. CAIN.

A heat treating process comprising main-

